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Avalanche Forecast

Archived

Dec 25th, 2019–Dec 26th, 2019

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Lizard-Flathead.

Snow continues to settle over a deep persistent weak layer, which very recently produced very large avalanches. Any additional load, such as a smaller avalanche, cornice failure, or person, could trigger large and destructive avalanches.

Confidence

Moderate - Uncertainty is due to how quickly the snowpack will recover and gain strength.

Weather Forecast

Wednesday Night: Mostly clear and starry. Alpine temperature -10 C. Southwest wind, 10-15 km/hr.

Thursday: Mostly cloudy with isolated flurries. Alpine temperature -10 C. Southwest wind, 20-30 km/hr.

Friday: Mainly cloudy with isolated flurries, trace to 5 cm. Alpine temperature -12 C. West wind, 15-25 km/hr.

Saturday: Sunny with cloudy breaks and isolated flurries. Alpine temperature, -10 C. West wind, 10-20 km/hr.

Avalanche Summary

Snow accumulation over the weekend overloaded deeply buried weak layers. A natural storm slab avalanche cycle to size 3 occurred Saturday and Sunday following intense and heavy loading from snow/rain and wind.

Explosives triggered very large (size 3-3.5) avalanches Saturday and Sunday, these avalanches failed on a deep persistent weak layer with some avalanche crowns over 2 m. On Monday and Tuesday explosives continued to produce large (size 2-2.5) deep persistent slab avalanches.

Snowpack Summary

The massive load of recent storm snow is settling around the region. More recent flurries have left 10-30 cm lower density snow on the upper snowpack. Winds are slowly redistributing loose snow. Between 1400-1600 m, this loose snow overlies a rain crust. Below 1400 m, a previously isothermal snowpack is recovering.

Weak facets and decomposing crust layers from November and October can be found 80-140 cm below the surface. The intense loading of storm snow overloaded these weak layers, producing very large (size 3) avalanches on Saturday and Sunday triggered by explosives. A complex avalanche problem has developed, check out latest forecaster blog here.

Snowpack depths range between 60-160 cm at higher elevations and taper rapidly below treeline.

Terrain and Travel

  • Cornice failure may trigger large avalanches.
  • Minimize exposure to overhead avalanche terrain, large avalanches may reach the end of runout zones.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.